This invention is directed to improvements in automatically operating air shut-off controls for hand tools, such as nut runners, equipped with air driven vane motors.
It is particularly concerned with shut-off controls of a type in which centrifugal forces developed by the motor are utilized in their operation. The general purpose of such controls is to cause flow of operating air to the motor to be automatically discontinued as the nut being run down reaches a predetermined torqued condition.
Tools of this general purpose and nature are known from U.S. Pat. Nos. 3,791,458; 3,785,442; and 3,904,305. The arrangements in these tools employ air transmitting control valves to which application of precise differential air pressures is required for their proper functioning in the system to effect the desired shut-off of operating air to the motor.
The mode of operation of these known shut-off controls, together with their particular arrangement of cooperating components is complex, and the structures are involved.
Further, these known controls include a centrifugally operable control device supported at one end to the rotor shaft, but lacking support at the opposite end. Because of this mode of support, the high speed to which the control device is subjected may result in undesirable vibratory action.
Accordingly, a general object of the present invention is to improve over these known tools. It is intended to provide an air shut-off control arrangement for such tools which is not complex or involved in the organization and mode of cooperation of its components; which is simple in the mode of operation of its valve elements; and in which a centrifugally operable control mechanism is adequately supported at both ends so as to avoid undesirable vibration.
In accordance with the invention there is provided a portable pneumatic nut running tool comprising an air driven torque transmitting motor, a primary and a secondary air feed passage connecting with the motor, a throttle valve operable from a closed normal position to an open condition to feed operating air to both the primary and secondary passages, a shiftable control valve normally blocking the secondary passage to flow of operating air to the motor, centrifugally operable means responsive to acceleration of the motor to shift the control valve to open the secondary passage to flow of operating air to the motor, a blocking valve movable from an open normal position to a position blocking the primary passage to flow of operating air to the motor, manipulative lever means movable through an initial angle to open the throttle valve and movable through a further angle to move the blocking valve to its position blocking the primary passage, spring means responsive to a predetermined degree of deceleration of the motor to return the control valve to its position blocking the secondary passage, and return spring means responsive to manual release of the lever means to return the throttle and blocking valves to normal.